Surgical, torque-transferring instrument including an associated tool

ABSTRACT

A surgical instrument includes a handpiece to which a handpiece shaft can be flanged, and a tool mounting for receiving a tool which can be rotatably supported in the handpiece shaft for axially securing the tool in the tool mounting and for transferring a torque to the tool. The tool mounting includes a sleeve-shaped entrainment shaft with a plug-in zone for a torsion rod and torque transmission and axial locking zones for the tool. The tool mounting also includes a closure sleeve surrounding the entrainment shaft that includes a distal blocking section which acts on the axial locking zone of the entrainment shaft for axially locking and releasing the tool, and a proximal arresting section acting on the plug-in zone of the entrainment shaft for arresting the tool mounting on the torsion rod to transfer torques and axial forces and for releasing the tool mounting from the torsion rod.

RELATED APPLICATIONS

This application is the U.S. National Phase of International ApplicationNo. PCT/EP2013/067639, filed Aug. 26, 2013, which in turn claims thebenefit of priority of German Application No. DE 10 2012 108 264.2,filed Sep. 5, 2012, the contents of both applications being incorporatedby reference in their entireties.

FIELD

The present invention relates to a surgical instrument for providing atorque as well as a driven tool which is rotatably supported in theinstrument handpiece or a handpiece shaft connected thereto and to whicha torque can be transmitted which is as high as possible.

BACKGROUND

In the advanced (minimally invasive) surgery, instruments are used forinstance for a chip-removing or material-removing machining of bones,cartilages etc., for example with arthroscopic operations, in spinalsurgery and similar orthopedic treatments, which comprise anergonomically shaped handpiece and an optionally exchangeable tool (suchas a milling cutter, turning knife, polishing head, etc.) which isrotatably supported in the handpiece at its distal end so as to be ableto be driven. Depending on the designated use and the intendedrotational speed, the tool drive is a hydraulic, pneumatic orelectromotive drive which is in operative connection with the tool via atorque transmission train (such as a gearing mechanism and/or a numberof shafts which may possibly be coupled to one another) within thehandpiece. The drives may be integrated in the handpiece or implementedas external drive units which are coupled to the handpiece via energysupply lines or torque transmission lines (e.g. flexible and elasticshafts); in this case, the handpiece essentially serves only foraccommodating the gearing mechanism or torque transmission train.

Tubular handpiece shafts are usually connected/mounted to the distalends of the handpieces, i.e. the ends facing the body, and depending onthe intended purpose said handpiece shafts have different shaft lengthsand shapes to advance to various places within a patient body. By way ofexample, there are straight or bow-shaped handpiece shafts or preferablythose which are cranked (angled) in the zone where they are fitted tothe handpiece; in said handpiece shafts, a torque transmission rod orshaft (in the following: torsion rod) is always supported. Saidrod/shaft has to be sufficiently stiff (resistant to torsion) in orderto be able to transfer the required torque to a tool which is distallyinserted therein or formed thereon (i.e. the rod needs to have asufficiently high torsional stiffness), but also has to be sufficientlyflexible, i.e. possess a certain bending flexibility, in order to becapable of following the curvatures of a (not straight) handpiece shaftroute also in the presence of a rotary movement.

For connecting the tool to the torsion rod supported in the handpieceshaft, a shaft coupling is provided for detachably receiving a toolshaft. In such arrangement, however, one problem is to provide such ashaft coupling for the possibly exchangeable tool within thesmall-diameter handpiece shaft with such a design that a safe andlong-lasting function of the surgical instrument is ensured even withsuch small handpiece shaft diameters and high rotational speeds,especially also with long handpiece shafts. Moreover, also the handpieceshaft should be exchangeably received on the handpiece in order to beable to realize different shaft lengths and shapes with a singlehandpiece. Here, the crucial point is the additional detachabletorque-based connection between the gearing mechanism/torquetransmission train accommodated in the handpiece and the torsion rodsupported in the shaft; on the one hand, said connection is required tobe closed in an easy and simple manner and on the other hand it issupposed to transfer sufficiently high torques. Finally, the operabilityof the instrument (including the process of exchanging a tool and/or ahandpiece shaft) should be simple and safe.

A surgical instrument of this kind and in particular a handpiece of sucha surgical instrument is known from EP 1 598 023 A2, for example.

In this special case, the known handpiece consists of a sleeve-shapedhandle portion (which could have any other handle shape, of course)which has a proximal end (facing away from the body) to which a linepackage for power supply (pressurized air, electrical current orhydraulic pressure) can be connected and a distal end (facing the body)to which a handpiece shaft is screwed (optionally in exchangeablefashion) by means of a union nut. The handpiece shaft has an outer andan inner shaft jacket which also serves for slidably and rotationallyguiding the torsion rod inserted therein. In the axial direction, theinner shaft jacket is subdivided in several segments between which oneball bearing each is inserted in the outer shaft jacket, said ballbearings supporting the torsion rod on the outer shaft jacket. A tool,preferably a milling head is fixed or formed on the distal end of thetorsion rod.

As can be taken from this reference, the tool is basically formed froman engagement or cutting head and the torsion rod, which are connectedto each other in one piece. Thus, the coupling between the tool and thegearing mechanism/torque transmission train within the handle portion isachieved exclusively in the area of the union nut. This means that thetool is a custom-made article which is especially adapted in its lengthto said one, specific handpiece shaft and cannot be used for otherhandpiece shafts having another length. It is obvious that such a designprinciple is expensive to manufacture as well as in providing it, as amatching tool has to be present or to be stored for each handpieceshaft.

The attached FIG. 1 schematically illustrates the longitudinal sectionof such a known surgical instrument in which a tool has already beeninserted.

According to that, the known tool comprises the tool shaft whichprojects out of the distal end of the instrument shaft or handpieceshaft so as to be rotatable and has its distal end provided with acutting head (not shown in further detail). The proximal tool shaft endillustrated in FIG. 2 in an enlarged view is provided with the knowntool shaft in the form of a sharpened wedge shape, forming two inclinedsurfaces (corresponding to a so-called dihedron) facing away from eachother and serving for introducing a torque. On the distal end portion ofsaid wedge shape, the tool shaft is formed with a circumferential groovewhich serves as an axial locking means as will be described below.

In accordance with the above tool construction, the known handpiece hasits distal end provided with an axially shiftable cap sleeve by means ofwhich the instrument shaft or handpiece shaft can be coupled to thehandpiece in torque-proof fashion. Within the handpiece in the area ofthe cap sleeve, a rotatably supported accommodation tube is providedwhich has its proximal end portion put into a rotary spindle and securedin torque-proof fashion therein by means of a cross pin.

Formed on the distal end of the accommodation tube are at least twodiametrically opposing holes which have clamping balls movably insertedtherein. A closure or clamping sleeve is supported so as to surround theoutside of the accommodation tube and so as to be axially shiftable; ina first axial position, said clamping sleeve unblocks the clamping ballsso that they can move radially outwards, and in a second axial positionit urges the clamping balls in radially inward direction. For the manualoperation of the clamping sleeve, a slider is also provided which issupported on the outside of the handpiece and connected to the clampingsleeve by means of a driving pin. In this context, it is to be notedthat the slider is spring-biased toward the second axial position of theclamping sleeve.

As can be further taken from FIG. 1, a torque transmission bolt isprovided within the accommodation tube so as to be relatively shiftablein axial direction; said bolt comprises a distally arranged, axiallyextending wedge-shaped notch which can be made to engage the wedge shapeof the tool shaft for torque transmission. The bolt is biased in distaldirection by means of a spring and is secured in the accommodation tubeby a cross pin in torque-proof manner.

According to said constructional design, the known tool—with its toolshaft ahead—has to be inserted into the handpiece shaft at the distaltip thereof and has to be axially shifted therein toward theaccommodation tube until the proximal tool shaft wedge (dihedron) restsagainst the clamping balls. At that moment, the clamping sleeve isaxially shifted to its release position via the slider, so that theclamping balls are displaced by the tool shaft wedge in radially outwarddirection and in this way is able to further advance into theaccommodation tube until it comes to lie in the notch of the torquetransmission bolt. If the slider is released again, the clamping sleeve(driven by the pretensioning spring) automatically returns to itsclamping position in which the clamping balls are urged radially inwardsinto the circumferential groove on the tool shaft and hence lock thetool shaft in axial position. In this way, a torque can be transferredfrom the rotary shaft through the cross pin, the accommodation tube, thefurther cross pin and the torque transmission bolt (torque transmissiontrain) to the tool shaft.

The known construction described above, however, has some particularfeatures which are in need of improvement:

The described cross pin connections result in a local weakening of thematerial in the torque transmission bolt as well as in the accommodationtube and also in the rotary shaft within the handpiece. In addition, thecross pins are quite thin and therefore prone to breakage. As a whole,the transferable torque is limited.

Furthermore, the wedge shape of the tool shaft is not very suitable fortransferring high torques, as the axially acting force amount results inthe tool-side wedge shape becoming disengaged from the notch of thetorque transmission bolt. Moreover, it has to be expected that theaccommodation tube is spread apart in the area of the notch.

Finally, the entire coupling-related mechanic system for connecting thetool shaft to the gearing mechanism/torque transmission train within theinstrument handpiece has been displaced to the area of the cap sleevewhere there is still a sufficient amount of radial clearance forreceiving the coupling elements. As a consequence, the tool shafts haveto span the full length of the instrument shafts or handpiece shafts.This means that special tools are required for each handpiece shaft.

SUMMARY

In the light of said prior art, it is the object of the presentinvention to provide a tool for a surgical torque-transferringinstrument as well as a system (surgical instrument) preferablyconsisting of an instrument handpiece and at least one (or more) tool(s) according to the invention, which each allow to achieve a betterfunctionality. Preferably, the instrument is supposed to be able totransfer high torques on the whole; more preferably, it should have aneasy and safe handling. One of the aims is to reduce the production andprovisioning costs for the system/instrument by using universal toolsfor different (exchangeable) handpiece shafts.

The above object as well as the other advantageous aims of the inventionare achieved by a generic system/instrument made up of a handpiece and apreferably exchangeable handpiece shaft.

Therefore, one aspect of the present invention is to provide a surgicaltorque-transferring instrument comprising a handpiece to which ahandpiece shaft is flanged or can be flanged (forming the handpieceshaft in one piece with the handpiece is also comprised), in which atool mounting is provided for selectively receiving a surgical toolwhich is rotatably supported in the handpiece shaft or can be rotatablysupported therein, in particular for axially securing the tool in thetool mounting as well as for transferring a torque to the tool.According to the invention, the tool mounting comprises inter alia thefollowing components:

-   -   a sleeve-shaped entrainment shaft comprising a proximal plug-in        zone for a torsion rod introducing a torque as well as distal        torque transmission and axial locking zones for the tool and    -   a closure sleeve surrounding the entrainment shaft in shiftable        manner and preferably in rotatable fashion, said closure sleeve        comprising a distal blocking section which acts on the axial        locking zone of the entrainment shaft for axially locking and        releasing the tool, and a proximal arresting section acting on        the plug-in zone of the entrainment shaft for arresting the tool        mounting on the torsion rod to transfer torques and axial forces        and for releasing the tool mounting from the torsion rod.

Due to the fact that torques are immediately transferred from theentrainment shaft to the tool (for instance by a form-fit between thetwo components), the number of components/elements which are involved inthe torque transmission flow is reduced, so that the radially availableinstallation space (within the handpiece shaft) can be optimally usedfor torque transmission. In addition, the torque transmission betweenthe torsion rod and the entrainment shaft occurs on the outercircumference of the torsion rod (by action of the closure sleeve) byutilization of a large lever arm in radial direction. As a consequence,it is possible to transfer comparatively high torques at this point.

It is preferred that one entrainment element, preferably severalentrainment elements spaced in circumferential direction is/are providedwhich is/are inserted in the plug-in zone in a form-fitting mannerbetween the entrainment shaft and the torsion rod (exclusively in itscircumferential peripheral area) and are radially secured towardsoutside by the closure sleeve in an axial locking position or can besecured in such manner. This means that the material of the torsion rodis weakened only to a minimum extent and in this way the torsion rod iscapable of transferring large torques without the need of radiallyexpanding it.

According to a further, possibly independent aspect of the presentinvention, provision may be made that the entrainment elements,preferably realized in the form of balls, or rollers, cylinders orbarrels rounded on the end face, are located in accommodation pockets(exclusively) on the outer circumference of the torsion rod as well asin radial apertures or openings in the plug-in zone of the closuresleeve, in order to transfer at least torques and preferably also axialforces from the torsion rod (directly) to the entrainment shaft. Thisallows to achieve a comparably extensive contact area between theentrainment elements and torsion rod as well as entrainment shaft, toavoid the entrainment elements from being sheared off with high torques.

For ease and simplification of the assembly of the tool mountingaccording to the invention, it may be preferably provided that theclosure sleeve has provided its proximal arresting section with at leastone fill opening and preferably a number of circumferential fillopenings for inserting the entrainment elements if the closure sleeve issituated in its one (combined) axial release position and rotary fillingposition. This means that fill openings are provided in the closuresleeve which overlap the apertures with the correct axial and rotationalposition with respect to the entrainment shaft and in this way allow theentrainment elements to be inserted into the apertures and the radiallyinternal pockets of the torsion rod. After completion of the fillingprocedure, the closure sleeve only has to be turned back (to itsexclusive axial release position) and then shifted to its axial toollocking position.

According to a further aspect of the invention, which may be possiblyclaimed in independent manner, provision may be made that the distaltorque-transferring zone (24 a) is formed by an axial longitudinal slitin the entrainment shaft which is formed like a sleeve at least in saidportion, producing two axially extending protrusions or tongues whichdefine a tool mounting gap and are provided for a form-fittingconnection with a tool inserted in the gap. In this context, it shouldbe mentioned that the two tongues are surrounded preferably by a radialbearing (ball bearing) at least comprising an inner race to avoid aradial spreading during torque transmission.

A further aspect of the invention which may possibly be claimed inindependent fashion may provide that the axial locking zone, which hasbeen already mentioned above, is arranged in the proximal extension ofthe torque-transferring zone, said axial locking zone consisting interalia of at least one radial through-hole, preferably a number ofangularly spaced radial through-holes receiving locking elementspreferably in the form of balls which are pushed radially inwards(against the tool shaft) by the closure sleeve in its axial lockingposition.

To this end, the closure sleeve has its distal end portion preferablyprovided with an inner radial widening for radially releasing the ballsin its axial release position and for filling the radial through-holeswith the locking balls in its axial release position and rotary fillingposition (according to above definition).

A further, possible independent aspect of the present invention mayprovide an accommodation chamber which is formed in the entrainmentshaft, is disposed proximal relative to the locking zone and holds afollower element which comprises an axial, preferably bolt-shapedengagement portion being urged in radial direction between thepreferably ball-shaped locking elements by an axially acting followerspring.

In this context, it is also advantageous if the follower element hassuch a design that it urges the locking elements radially outward if thetool is not inserted and in doing so retains the closure sleeve in itsaxial release position, and is axially shifted against the followerspring by the insertion of a tool in order to allow a radial inwardmotion of the locking elements for axially locking the tool as well asan axial displacement of the closure sleeve into its locking position inwhich the locking elements continue to be pushed radially inward againstthe tool.

This measure creates a sort of semi-automatic tool mounting whichremains at first in its release position in which a tool can beinserted; it is by the insertion operation that a locking of the toolfor a secured torque transmission is initiated (occurs) automatically.By manually and axially shifting the closure sleeve into its releaseposition, the tool is released again for its removing.

Finally, and according to a further aspect of the invention possibly tobe claimed independently, it may be made provision as a basic principlethat a torque introduced by the torsion rod is transferred to theentrainment shaft through a number of entrainment elements which are(exclusively) circumferentially arranged on the torsion rod, and fromsaid entrainment shaft directly to a tool received therein, the axialsecurement of the tool in the entrainment shaft being effected outsidesaid torque transmission train by axially acting locking elementsbetween the entrainment shaft and the tool.

The invention will be explained in more detail below by means of apreferred exemplary embodiment as well as several variants with respectto the accompanying Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the longitudinal section of a surgical instrument of thekind (including handpiece, handpiece shaft and tool) as it is also knownfrom prior art and is to serve as a reference for a better illustrationof the invention,

FIG. 2 shows an enlarged view of the proximal shaft end portion of atool for the surgical instrument according to FIG. 1,

FIG. 3 shows the longitudinal section of a surgical instrument/systemincluding handpiece, handpiece shaft and tool according to a preferredexemplary embodiment of the present invention,

FIGS. 4 a, 4 b show an enlarged view of the proximal shaft end portionof a tool, according to the invention, for a surgical instrumentaccording to FIG. 3,

FIG. 5 shows an enlarged longitudinal section view of the instrument,according to the invention, in the area of the tool lock (of the toolmounting/tool lock),

FIG. 6 shows an enlarged cross-sectional view of the tool mounting alongthe sectional line A-A according to FIG. 5, with the tool having beeninserted already,

FIGS. 7 a and 7 b each show a longitudinal section view of a first andsecond variant, according to the invention, of the bearing of the toolor the tool mounting in a comparison,

FIG. 8 shows an enlarged view of the proximal tool shaft end portionaccording to a variant which represents an alternative to FIG. 4,

FIG. 9 shows an example, according to the invention, of a codingpossibility of different tool shafts for the foolproof use in differenttool mountings (different handpiece shafts/handpieces according to theinvention),

FIG. 10 illustrates two examples of a correct and an incorrect selectionof a tool for an instrument handpiece/handpiece shaft according to theinvention (comprising a specific mounting) corresponding to the codingof the invention according to FIG. 9,

FIG. 11 shows the longitudinal section of the surgical instrumenthandpiece of the invention (according to FIG. 1) in the area of the toollock (tool mounting/tool coupling) without any tool,

FIGS. 12 and 13 (chronologically) describe the assembly process forproviding the tool lock (tool mounting) according to FIG. 12,

FIG. 14 shows the cross-section of a cloverleaf coupling according tothe invention for a (detachable) (torque transmission) connectionbetween the tool lock (tool mounting or torsion rod) and an output shaftwithin the surgical instrument handpiece for exchanging the distalhandpiece shaft,

FIG. 15 shows a male and a female part of the cloverleaf couplingaccording to FIG. 14 and

FIG. 16 shows the process of inserting a tool according to the inventioninto a tool mounting according to the invention step by step.

DETAILED DESCRIPTION

The surgical instrument or instrument system according to the inventionconsisting of an exchangeable (rotary) tool, a (universal) instrumenthandpiece and a possibly exchangeable handpiece shaft (including atorsion rod supported therein) basically includes four partial aspectsaccording to the invention which can be claimed in the context of thisinvention independently or in combination with one another and aredescribed in detail below. These partial aspects include

-   -   the configuration of the proximal shaft end portion of the tool,        according to the invention, of the present instrument system,    -   the creation of a plug-in securing means in the form of a tool        coding means for avoiding a fault in terms of selecting or using        a tool,    -   the construction of the tool lock according to the invention (or        also of the tool mounting) within the handpiece shaft of the        instrument handpiece as a part of the torque transmission train        to the tool (for coupling the tool to the torsion rod within the        handpiece shaft) as well as the tool lock construction in its        operating portion and    -   the development of a coupling/torque-proof connection between        the tool lock (tool mounting) and the torsion rod within the        handpiece shaft and an output shaft within the handpiece for        facilitating the replacement of the distal handpiece shaft        (including the tool lock supported therein and the torsion rod).

Tool According to the Invention Comprising Axially Separated TorqueTransmission Means, Tool-Related Screw-in/Alignment Means and AxialLocking Means

According to FIGS. 4 a, 4 b and 8, the tool 1 according to the inventionsubstantially consists of a distal engagement segment or portion (facingthe body) such as a drilling, milling, grinding or polishing head 2 towhich a tool shaft 4 is attached preferably in the form of asubstance-to-substance bond (or soldered, welded, pressed, etc.) whichextends in proximal direction (facing away from the body). Said toolshaft 4 has a proximal end portion 6 for the torque-proof insertion ofthe tool 1 in a tool mounting (tool lock) of a surgical instrumenthandpiece or a handpiece shaft connected thereto as well as for an axialsecuring in the tool mounting.

To this end, the tool shaft 1 has its proximal end portion 6 subdividedin three functional areas which are axially spaced from one another (insuccession) and are described in the following in chronological orderstarting from the distal end of the tool shaft end portion 6 (accordingto FIGS. 4 a, 4 b and 8 the left-hand end of the proximal end portion6).

As can be taken from FIGS. 4 a, 4 b and 8, the entire tool shaft 4according to the present invention first consists of a distal,essentially non-profiled shaft portion (directly adjoining theengagement segment 2), as well as an adjoining proximal shaft endportion 6 which for its part is serially subdivided in a distal portion6 a having a large shaft diameter and an external, profiled area as wellas a proximal portion 6 b having a small shaft diameter. The diameterratio between the large and small shaft diameters D:d within theproximal shaft end portion 6 amounts to approximately 2:1. This meansthat the small shaft diameter d is substantially less than or equal tothe half of the large shaft diameter D. More specifically, d<=0.6 Dshall apply. Here, the large shaft diameter D is not formed so as tocontinuously taper toward the small shaft diameter d, but there is aradial shoulder 6 c between the two shaft portions 6 a, 6 b of differentdiameters, optionally with a small inner radius for avoiding any notcheffect.

In the area of the radial shoulder 6 c, the large-diameter shaft portion6 a is formed according to FIG. 4 a so as to have two diametricallyopposing contact surfaces or planes 8 (a so-called dihedron), whichapproach each other in wedge-shaped manner toward the radial shoulder 6c and serve for introducing a torque into the tool shaft 4. Thesecontact planes 8 may be formed in particular by grinding/milling orpressing/forging the initially unprofiled, round tool shaft 4.Additional glide surfaces or planes 10 (produced preferably in the samemanner as the contact surfaces 8) are formed on the axial side edges ofeach contact surface 8 (in the region of the radial shoulder 6 c), whichare each aligned at an angle to the associated contact surface 8 andextend from an axial center region of each of the contact plane sideedges toward the radial shoulder 6 c in wedge-shaped fashion. Thisresults in a shaft profile having six surfaces in the area of the radialshoulder 6 c; said six surfaces consist of the two diametricallyopposing contact planes 8 (dihedron) and, in the circumferentialdirection at both sides of each contact plane 8, respective glide orscrew-in planes 10 breaking the corresponding side edge of therespective contact surface 8 in the area of the radial shoulder 6 c andhence gradually reducing the width of the respective contact plane 8toward the radial shoulder 6 c.

According to FIGS. 4 a and 4 b, two notches or pockets 12 diametricallyarranged on the circumference of the shaft are formed on (preferablymilled into) the proximal end of the small-diameter shaft end portion 6b, whereby axially acting undercuts are formed on the shaft surface. Asan alternative to these notches 12 and according to FIG. 8, it is alsopossible to produce a surrounding groove 12 a on the proximal end of thesmall-diameter shaft end portion 6 c by use of a lathe, whose groovedepth essentially corresponds to the notch depth according to FIG. 4 a,4 b. These notches 12 or the circumferential groove 12 a serve(s) foraxially locking the tool shaft 4 within a tool mounting as it will bedescribed in the following.

The previously described shaft construction notably in the profiled toolshaft end portion 6 allows to achieve some advantages over the prior artaccording to FIGS. 1 and 2, which contribute to increase the maximumtransferable torque from the torsion rod within the handpiece shaft tothe tool 1:

-   -   Due to the basic separation of axial securing/locking section        and torque entrainment section (with interposed screw-in aid) in        two (possibly three) axially spaced shaft portions, these        functional sections can be optimized independently of one        another.    -   Here, the crucial point is that the functional section “locking”        6 b is proximally arranged with respect to the functional        section “torque entrainment” 6 a. This allows to realize the        locking portion 6 b, which is not subjected to torsion/torque,        with a small diameter as compared to the torque entrainment        portion 6 a and to form the radial shoulder 6 c in this way.    -   The radial shoulder 6 c in turn allows to form (to mill off),        distally to the small-diameter locking portion 6 b, two contact        or torque transmission planes 8 with a larger axial length, in        order to enlarge their respective surface area with respect to        the prior art. Further, the radial shoulder 6 c allows (as is        illustrated in particular in FIG. 6) to remove in its region        such a large amount of shaft material for forming the contact        planes 8 that the remaining shaft diameter (in the region of the        radial shoulder) between the two (wedge-shaped) planes 8 is        nearly reduced to the half. This means that according to FIG. 6        the diameter Dm which can be utilized for torque transmission        approaches the large shaft diameter D. If the dihedron formed in        such a way is pushed into an axial gap of an entrainment shaft        (which is described below), there is produced according to FIG.        6 a full circle with an optimal leverage ratio for torque        transmission.    -   Up to now, the axial locking section according to FIGS. 1 and 2        has been arranged between the functional section “torque        entrainment” and the tool engagement segment, limiting the        maximum axial extent of the functional section “torque        entrainment”. Due to the resulting steeper wedge shape of the        two contact planes, large axial forces act on the axial locking        section. In addition, there is a weakening of the material of        the locking portion arranged in the flow of torque. Now,        provision is made to place the axial locking 6 b proximal to the        torque entrainment 6 a (i.e. not between the torque entrainment        and the engagement segment) outside the flow of torque. This        allows to realize the wedge shape of the two contact planes 8 as        a whole in a more flat design (with larger axial extension),        reducing axial forces during torque transmission. Thus, the        required (radial) installation space for the axial locking 6 b        can be made smaller (a small tool shaft diameter d is possible).    -   Finally, forming the radial shoulder 6 c between the functional        sections “torque transmission” 6 a and “axial locking” 6 b        offers the possibility to arrange additional glide planes 10 as        screw-in aid in the functional section “torque transmission” 6        a. These glide planes 10 are each formed at both axial sides of        the two contact planes 8 so as to be wedge-shaped, too, and        break the side edges of the contact planes 8 in the area of the        radial shoulder 6 c, i.e. they are aligned at an angle relative        to the respective contact plane 8. These glide planes 10 serve        to orient the tool shaft 4 in the circumferential direction        during inserting it in a tool mounting of the handpiece, to be        more precise in such a manner that the two contact planes 8 are        correctly guided into the tool mounting.

Tool According to the Invention Comprising a Tool Coding Means

As already explained above, an essential feature of the presentinvention is to arrange the functional section “axial locking” 6 bproximal to the functional section “torque transmission” 6 a.Furthermore, the tool shaft 4 according to the invention may alsocomprise all other features according to the previous description; thesefeatures, however, are only optional for the following inventive aspect“tool coding means”.

Basically, a user wishes to minimize or eliminate malpractices inparticular as a consequence of wrong surgical tools. This may beeffected for instance by visual identifiers on the individual tools; inthis case, however, the “human” factor cannot be eliminated as a sourceof error, which means that visual identifiers may be overlooked ormisinterpreted/mixed up in reality, so that errors may occur during theselection of a specific tool which are detected only with its use andpossibly too late. This source of error is the more important, thehigher is the number of different tools which can be assigned to auniversal handpiece in the context of an instrument/instrument system.In this case, it is thus advantageous and desirable if only a limitednumber of tools can be used for certain surgical intended purposesdepending on a specific handpiece shaft (comprising an internallysupported torsion rod) attached to the universal handpiece.

FIGS. 9 and 10 illustrate an advantageous variant of a tool coding meansaccording to the invention, which allows to avoid the wrong selection ofa tool.

The way of arranging the functional section “axial locking” 6 b proximalto the functional section “torque transmission” 6 a in such a mannerthat the former does not serve for transmitting any torque offers thebasic (optional) possibilities to alter the axial length and/or the(small-diameter) shaft diameter d of said functional section 6 b withouthaving an (adverse) influence on the functional section “torquetransmission” 6 a. Thus, it is made possible to provide (or to combine)at least two (or more) different axial portion lengths (i.e. axialdistance between radial shoulder 6 c and radial pocket/circumferentialgroove 12/12 a or the axially acting undercut) and/or at least two (ormore) different (small-diameter) shaft diameters d, which are able tofunctionally cooperate only with correspondingly dimensioned toolmountings.

By way of example, FIG. 9 shows the two combinations “short lockingportion” with “small shaft diameter” and “long locking portion” with“larger shaft diameter” with respect to the functional section “locking”6 b. Accordingly, the tool mounting (which will be described in detailbelow) according to FIG. 10 is basically formed such that the smallershaft diameter indeed can be inserted in the mounting for the largershaft diameter for torque transmission, but there will be no axiallocking and therefore the tool 1 can again be retracted during checkingthe correct fit of the tool (upper picture). If the larger shaftdiameter is inserted into said tool mounting, however, the axial lockingwill occur (second picture from above). In return, a mounting providedfor the smaller shaft diameter does not allow to insert the larger shaftdiameter at all (lower picture), whereas the smaller shaft diameter canbe inserted and axially locked (second picture from below).

Here, reference is made to the fact that the length and the shaftdiameter of the functional section “axial locking” 6 b represent onlytwo coding parameters which can be detected in a particular simplemanner, but which can also be replaced or supplemented by otherparameters. By way of example, the circumferential position of thepockets 12 with respect to the two contact planes 8 may serve forallowing a locking process only in the presence of the correctpredetermined relative position (with a correspondingly correctorientation of the contact planes 8 relative to the tool mounting). Theshape of the pockets 12 may also be altered, namely in such a mannerthat only compatible shapes on the part of the mounting result in areliable axial locking. Finally, the portion “axial locking” 6 b may beformed so as to comprise an additional shape (not illustrated) whichcooperates according to the “key-keyhole-principle” with a correspondingshape in the tool mounting to allow the insertion of the tool shaft 4(e.g. tongue-and-groove arrangement).

Handpiece Shaft Comprising the Tool Mounting (or Also Tool Lock)According to the Invention

A tool mounting to be accommodated in a handpiece shaft, in particularfor a (unitary) tool according to the previously described first and/orsecond aspect(s) of the invention has to meet several requirementssubstantially comprising the following:

-   -   Small radial dimensions to allow for their accommodation in a        handpiece shaft which is narrow as is well-known.    -   A transfer of a sufficient working torque to the tool.    -   An ergonomically favorable and simple manual operation at least        for releasing the tool inserted therein and preferably an        automatic process of locking the tool (semi-automatic tool        mounting).    -   Protecting the tool mounting and the tool in operation against        self-acting dismantlement (such as in the presence of        vibrations, shocks and/or impacts) for increasing the        reliability of the instrument.    -   Simple and non-destructive assembly and disassembly of the        mounting for cleaning or maintenance purposes, for instance.

The purpose of such a mounting within the handpiece shaft basicallyconsists in displacing the tool mounting by any desired amount (and asfar as possible) in distal direction, in this way limiting the toolshaft to an optimum (unitary) length with respect to the bending forceswhich are to be expected during use of the tool. This allows to providesuch a (unitary) tool for different lengths and shapes of the shaft,with the shaft length between the handpiece and the tool mounting beingspanned by a possibly bendable/flexible or rigid torsion rod supportedin the handpiece shaft.

The known tool mounting schematically illustrated in FIG. 1 indeed hasthe potential regarding its spatial (in particular radial) dimensions tobe installed within a handpiece shaft which is known per se and is ofcommon design. However, in particular the cross pins for the connectionof the accommodation tube with the torsion rod as well as for thetorque-proof coupling of the accommodation tube with the torquetransmission bolt supported therein and acting on the tool eachrepresent a weak point in the torque transmission train, as has alreadybeen mentioned at the outset.

As shown in detail in FIG. 1, the inside torque transmission bolt iscoupled at least to the outer accommodation tube by means of the one(thin) cross pin fitted in a transverse longitudinal hole formedtherein. Such a (thin) cross pin is not able to reliably transfer amaximum torque which would be suitable for all purposes. In addition,the holes for the cross pin weaken the components which are to beconnected and are very small anyway, i.e. the accommodation tube and thebolt. In addition and as already explained above, a further cross pin isprovided for coupling the accommodation tube to the input or torsionrod, which causes the same problems. Notwithstanding the above, aprocess of connecting three components by means of the mentioned crosspins is very difficult and time-consuming in terms of manufacturing andassembly technology, especially with small dimensions as is the casewith the generic handpiece shafts of the relevant known design. Thus, itis desirable to provide a tool mounting in particular for a tool havingthe structure described above, by means of which these problems aresolved.

FIG. 11 shows a preferred exemplary embodiment of such a tool mounting20 according to the invention, whose components are described below indetail as well as in terms of their cooperation with the tool 1 which isdescribed at the outset.

First, the tool mounting or tool lock 20 of the invention and accordingto the preferred exemplary embodiment of the present invention comprisesa radially inner tool accommodation tube (in the following referred toas an entrainment shaft) 22 comprising, at its distal end, a(beak-shaped) distal torque transmission portion and locking portion 24slotted in the longitudinal direction; in its slotted torquetransmission zone 24 a (see also FIG. 6), said portion 24 has an outerdiameter which is adapted to the large-diameter tool shaft portion 6 a,and in its adjoining locking zone 24 b it has an inner diameter adaptedto the small-diameter tool shaft portion 6 b. In this arrangement, thelongitudinal slit 26 forms a slit width into which the tool shaft 1 canbe inserted in the area of the two wedge-shaped contact planes 8 (seeFIG. 6), so that the tool-side contact planes 8 rest against thebeak-shaped axial protrusions 28 of the torque transmission zone 24 awith extensive contact and together form a closed full-round profile(see FIG. 6).

The locking zone 24 b is proximally adjoined by a cylindrical boltmounting portion 24 c which has a somewhat larger inner diameter thanthe locking zone 24 b (the bolt 30 supported therein is referred to as afollower element below), with development of an inner radial shoulderwhich serves as an axial stop for the follower element 30 in distaldirection. To this end, the follower element 30 has a distal portion 30a comprising an outer diameter corresponding to the small-diameter toolshaft portion “locking” 6 b, which can thus be moved into the lockingzone 24 b of the entrainment shaft 22, as well as a proximal portionwith a larger outer diameter 30 b, where the follower element 30 isguided in the entrainment shaft 22 in sliding manner. Formed between thetwo portions 30 a, 30 b of the follower element 30 is an outer ringshoulder which cooperates with the inner ring shoulder of theentrainment shaft 22 in distal direction.

Finally, a follower spring 32 for the follower element 30 is provided inthe mounting portion 24 c; said follower spring biases the followerelement 30 in distal direction and in this way urges it against theinner ring shoulder in the entrainment shaft 22. In this position, thesmall-diameter distal portion 30 a of the follower element 30 iscompletely retracted in the locking zone 24 b of the entrainment shaft22.

It should be mentioned here that the locking zone 24 b of theentrainment shaft 22 is provided with a number (at least one) of radialthrough-holes 34 which are uniformly spaced along the circumference andserve for receiving locking balls 36 for the inserted tool 1, as will bedescribed below.

In the proximal prolongation of the mounting portion 24 c for thefollower element 30, the entrainment shaft 22 forms a coupling/plug-inportion 24 d for a drive/torsion rod 60, the latter being rotatablysupported in a handpiece shaft (not illustrated in FIG. 11, but see FIG.3, for example) of a (universal) handpiece.

In the area of this plug-in portion 24 d, also the entrainment shaft 22comprises a number (at least one) of radial openings or apertures 38which are uniformly spaced along the circumference and lie on a circularplane; said apertures have an approximately oval cross-section extendingin axial direction of the entrainment shaft 22 in each case. Theseradial openings 38 serve for receiving preferably oval rolling bodies 40(referred to as entraining elements in the following) via which theentrainment shaft 22 is coupled to the inserted torsion rod 60 inaxially fixed and torque-proof manner, which will be described in moredetail below. It should be noted here that balls may also be usedinstead of oval (cylindrical) rolling bodies with rounded end faces.

At the proximal end of the plug-in portion 24 d, the entrainment shaft22 further comprises a circumferential radial protrusion 42 which servesas a spring seat of an outer closure spring 44.

A closure sleeve 46 is supported around the entrainment shaft 22 so asto be rotatable and axially shiftable. Said sleeve has a distal ballreleasing zone 46 a with a large inner radius and a proximally adjoiningball retaining zone 46 b with a small inner radius, which is also guidedon the outside of the entrainment shaft 22 in sliding manner.

Formed in a proximal end portion of the closure sleeve 46 is a number(preferably two) of radial through-holes 48 with a longitudinally oval(or round) cross-section, which serve for filling the apertures 38provided in the entrainment shaft 22 with the oval/barrel-shaped,rounded rolling bodies 40. Each of said oval (larger length than width)through-holes 48 of the closure sleeve 46 is prolonged to form amounting pocket on the inner circumference of the closure sleeve 46, sothat the closure sleeve 46 can axially move over the already insertedrolling bodies/entraining elements 40 and prevent them from falling out.At the same time, the mounting pockets have such a shape that theclosure sleeve 46 can be rotated by a defined angle with respect to theentrainment shaft 22, so that according to the following description therolling bodies 40 and also the locking balls 36 cannot fall out any moreeven if the closure sleeve 46 is moved back to an axial releasingposition.

Finally, the closure spring 44 is arranged axially between the closuresleeve 46 and the outer radial protrusion 42 of the entrainment shaft22, and urges the closure sleeve 46 in distal direction into an axiallocking position.

The assembly and the mode of operation of the tool mounting 20 accordingto the invention is explained in more detail below on the basis of FIGS.11 to 13 in connection with FIG. 5.

According to FIGS. 12 and 13, fitting the tool mounting 20 to a torsionrod 60 begins with slipping the outer closure spring 44 over theentrainment shaft 22; subsequently, the closure sleeve 46 is put on theentrainment shaft 22 from distal direction, so that the outer closurespring 44 comes to lie between the closure sleeve 46 and the outerradial protrusion 42 on the entrainment shaft 22 (see illustrations 1and 2 of FIG. 12).

As a next step, the closure sleeve 46 is pushed against the outerclosure spring 44 into its axial filling or releasing position, wherebythe through-holes 34 in the locking zone 24 b of the entrainment shaft22 are exposed. At that moment, the locking balls 36 can be placed insaid through-holes 34 through an assembly groove provided inside theclosure sleeve 46, said locking balls projecting radially inwards (seeillustrations 3 to 6 of FIG. 12). Subsequently, the closure sleeve 46can be released whereby it is axially moved to the ball locking positionby means of the outer closure spring 44, in which position the closuresleeve 46 is shifted over the locking balls 36 and hence prevents themfrom falling out radially. The locking balls 36 simultaneously serve asan axial stop for the closure sleeve 46, which has its distal innercircumference provided to this end with a small inner radial shoulderaxially resting against the locking balls 36 in the retaining or lockingposition of the closure sleeve 46 (see illustration 7 of FIG. 12). Withthis, the preliminary assembly of the tool mounting 20 according to theinvention is completed.

FIG. 13 illustrates the process of fitting the tool mounting 20 to atorsion rod 60.

First, the follower element 30 and then the inner follower spring 32 isinserted into the entrainment shaft 22 from proximal direction, thedistal portion 30 a of the follower element 30 axially resting againstthe locking balls 36. Subsequently, the torsion rod 60 is put into theentrainment shaft 22 from proximal direction. The torsion rod 60 has itsdistal end formed like a radial shoulder 62 as a spring seat for thealready inserted inner follower spring 32. Further, the torsion rod 60comprises at its distal end portion a number of outer pockets 64 whichare uniformly spaced along the circumference and serve for receiving theentraining elements (oval rolling bodies) 40. Finally, thecircumferential side of the torsion rod 60 optionally forms a shaft step66 working as an axial stop for the entrainment shaft 22.

As soon as the entrainment shaft 22 rests against the optional axialstop 66 of the torsion rod 60, the radial outer pockets 64 of thetorsion rod 60 exactly overlap the proximal apertures 38 of theentrainment shaft 22 as well as the fill openings 48 of the closuresleeve 46 pushed into the axial fill/releasing position (seeillustrations 8 to 10 of FIG. 13). This is the time to insert the ovalentraining elements 40 via the fill openings 48 of the closure sleeve 46into the apertures 38 of the entrainment shaft 22 as well as into theouter pockets 64 of the torsion rod 60 (see illustration 11 of FIG. 13).As a final step, the closure sleeve 46 is released which isautomatically moved axially to the locking position in distal directionby the closure spring 44; in said locking position, the closure sleeve46 has moved over the locking balls 36 and the entraining elements 40and hence prevents them from falling out radially. As a last step, theclosure sleeve 46 is rotated by a defined angle with respect to theentrainment shaft 22. This allows to prevent the balls 36 and preferablyalso the entraining elements 40 from unintentionally falling out throughthe fill openings 48 of the closure sleeve 46 even if the closure sleeve46 is again retracted into the ball releasing position during normaloperation. This means that the axial position of the closure sleeve 46for filling it with the entraining elements 40 as well as radiallyreleasing the balls 36 during insertion of a tool 1 is preferably thesame. The angular position of the closure sleeve 46 with respect to theentrainment shaft 22 in the filling position, however, is different fromthe angular position in the releasing position.

With this, the process of fitting the tool mounting 20 to the torsionrod 60 is completed.

As is made plain by the above description of the assembly process,radially outer entraining elements 40 preferably in the form of ovalrolling bodies are provided for a torque transmission from the torsionrod 60 to the entrainment shaft 22. Thus, these elements have a largeeffective force application surface and thus are capable of transferringsubstantial torques without getting sheared off. At the same time, theentraining elements serve for axially securing the tool mounting on thetorsion rod. Owing to the radially outer positioning, a maximal leveragefor torque transmission is achieved, too.

According to the invention, the torque is transferred to the tool shaft4 not via the follower element (bolt) 30 as is the case with thementioned prior art, but directly via the entrainment shaft 22. Thisreduces the number of the components incorporated in the torquetransmission train, which simplifies the assembly as a whole.

The mode of operation of the tool mounting 20 according to the inventionis explained in more detail below on the basis of FIGS. 5, 7 a, 7 b and16.

First, it should be noted that the tool mounting 20 has to be rotatablysupported within a handpiece shaft which can be coupled to a universalhandpiece. To this end, a radial bearing (KL) 50 such as a ball, rolleror needle bearing comprising an inner and outer race is preferablyprovided and fitted to the entrainment shaft 22 in the torquetransmission zone 24 provided with the longitudinal slit; thus, itcounteracts a spreading apart of the beak-shaped axial protrusions 28 ifa torque is transmitted to the contact planes 8 of the tool shaft 4. Inaddition, the support/cantilevered ratio being present on the tool shaft4 is improved by such a ball bearing (KL) 50 in the longitudinallyslotted torque transmission zone 24 a, as is shown in particular inFIGS. 7 a and 7 b.

FIG. 7 a shows the installation situation of a tool 1 in a tool mounting20 according to the invention comprising a radial bearing (KL) 50 in thetorque transmission zone 24 a of the entrainment shaft 22. As can betaken from this Figure, the tool shaft 4 extending distally out of thehandpiece shaft 70 is supported by at least one distal bearing(preferably two distal bearings) 72 and at least one proximal bearing50, 74, in order to absorb tool contact forces and cutting forces whichact on the tool shaft 4 as bending forces. Accordingly, if the at leastone proximal radial bearing 50 is positioned in the torque transmissionzone 24 a of the tool mounting 22, there is a support length between thedistal and proximal bearing 72, 50 which is significantly larger thanthe cantilevered length between the distal bearing 72 and the toolengagement segment 2.

On the contrary, FIG. 7 b shows a reference example in which the bearing74 provided distal to the torque transmission zone 24 a is assumed asthe proximally last radial bearing (actually no additional ball bearing(KL) 50). In this case, the support length is shortened as compared tothe cantilevered length. It is obvious that the load on the radialbearings 72, 74 is enlarged in the latter case according to FIG. 7 b andhence show higher wear. The maximum admissible load is small as well.

The procedure of inserting the tool 1 according to the invention intothe tool mounting 20 according to the invention is illustrated in detailin FIG. 16.

First, the tool shaft 4 is approached to the torque transmission zone 24a of the tool mounting 20, possibly even in an incorrect relativerotational position; in this case, the tool-side glide surfaces 10 makecontact first with the two beak-shaped axial protrusions 28 of the toolmounting 20. Due to their orientation, the entrainment shaft 22 isrotated automatically until the two contact planes 8 face the radiallyouter axial protrusions 28. Now, the tool shaft 4 can be fartherinserted into the tool mounting 20, the tool-side contact surfaces orplanes 8 being guided in sliding manner between the beak-shaped axialprotrusions 8. The radial bearing 50 which is also shown in FIG. 16prevents the beak-shaped or forked axial protrusions/lugs 28 from beingspread apart.

For inserting the tool shaft 4, the closure sleeve 46 first is in itsretracted releasing position in which the locking balls 36 can be pushedradially outward. This is effected by the follower element 30 (bolt)whose distal portion 30 a is pushed radially between the locking balls36 by the follower spring 32, keeping said balls in radially outwardposition. The balls 36 which are pushed radially outwards will then keepthe closure sleeve 46 axially in its releasing position.

During the penetration of the tool shaft 4 into the tool mounting 20,however, the end face of the tool shaft-side locking portion 6 b hitsthe follower element 30 and displaces it in axial direction against thepretensioning force of the follower spring 32 until thepockets/circumferential groove 12/12 a are/is situated in the lockingportion 6 b of the tool shaft 4 in the area of the locking balls 36. Inthis moment, the balls 36 are pushed inwards and thus come to lie in thecircumferential groove 12 a or the pockets 12 of the tool shaft 4 whichis effected by the closure sleeve 46 due to the axially acting springpreload and a corresponding conical shape on the inner circumferentialside of the closure sleeve 46 (not shown in further detail). At the sametime, the closure sleeve 46 due to the spring preload is moved furtherin distal direction to its locking position. With this, the tool 1 isaxially secured, and a torque can be transmitted from the torsion rod 60via the entraining elements 40 and the entrainment shaft 22 to thecontact planes 8 of the tool shaft 4.

In order to remove the tool 1, the closure sleeve 46 is (manually)retracted against the closure spring 44 into the releasing position inproximal direction to release the locking balls 36 radially. If the toolshaft 4 is then pulled out of the mounting 20, the follower element 30follows the tool shaft 4 automatically due to the follower spring 32 andin this way comes to lie radially between the locking balls 36 in orderto keep them pushed radially outward. This is why the tool mounting 20remains in this releasing position to axially lock a newly inserted toolshaft 4 in automated fashion. Thus, the present tool mounting 20according to the invention may also be referred to as a semi-automatictool mounting (automatic locking and manual release).

Coupling Between the Tool Mounting or Torsion Rod and a Handpiece-SidedGearing Mechanism Train

As already explained at the outset, one aspect of the present inventionis the possibility to use always the same tool for different handpieceshafts. The handpiece shafts have such a construction that they can becoupled to a single, universal handpiece in which the tool drive and/orthe torque transmission train/gearing mechanism is/are housed. Thismeans that a torsion rod has to be pre-installed within the respectivehandpiece shaft; the distal end of said torsion rod has to be providedwith the tool mounting preferably according to the above description andits proximal end has to be provided with a coupling which in the courseof firmly coupling the handpiece shaft to the handpiece (preferably toits housing) simultaneously comes into operative engagement with thetorque transmission train to allow a torque transmission to the torsionrod.

In the first place, a coupling of this type has to transfer torques, butmust also permit an axial displacement of the drive shaft so that thetool mounting can be unlocked and dismounted, for example. Moreover, thecoupling should possess sufficient guiding qualities in order to be ableto save—at least in this area—further radial bearings (ball bearings)for supporting the coupling.

Up to now, the coupling in question between the torsion rod (within theexchangeable handpiece shaft) and the torque train (within thehandpiece) has been realized by a so-called dihedron which is comparableto the previously described torque transmission portion, according tothe invention, between the tool shaft and the tool mounting. However,such a coupling (without surrounding radial bearing) has the basicproblem of an insufficient torsional rigidity in the given (narrow)constructional space, which might result in an early failure of thecooperating coupling components. In addition, said construction achievesonly insufficient guiding qualities.

An alternative to the mentioned dihedron is the commonly knowncross-type solution. In this case, the male coupling piece is providedon the side of the torsion rod with webs crossing at an axially centralposition and capable of being inserted into a correspondingly shapedfemale coupling piece, whereby the surface area, available for torquetransmission, on the side faces of each web can be enlarged as a whole.This solution, however, is also afflicted with problems insofar as thereis no optimum distribution of the torsional rigidity between the maleand the female coupling piece, so that maximum transferrable torque islimited here, too.

In order to solve this problem, a cross-sectional geometry for thecoupling pieces (male and female) is required which makes optimum use ofthe given constructional space in the case of a surgical handpiece ofthe relevant kind with respect to the torsion-related moment of area, atthe same time allows an axial displacement of the two couplingcomponents relative to each other and does not come into a self-lockingcondition due to the special shape.

In the course of developing the coupling according to the invention, ithas turned out that the form fit for torque transmission is the less,the more the entrainment contour resembles a circle. Further, the lowerthe number of corners of the entrainment contour, the more form-lockingis the coupling combination (with decreasing section modulus). As awhole, a cloverleaf coupling 80 comprising four lobes turns out to be aparticularly advantageous cross-sectional shape of the coupling for asurgical instrument of said kind. FIG. 14 illustrates an optimizedcross-section of a four-lobed cloverleaf shape according to a preferredexemplary embodiment of the invention.

Accordingly, the cross-sectional shape, according to the invention, ofthe coupling 80 is based on four equal circles 82 with a small radiusRe, which define the four corners of the coupling shape and are arrangedso as to be angularly offset by 90° relative to each other. The distanceof the respectively neighboring centers of the circles which are withinthe coupling shape is slightly smaller as the unitary circle diameterRe, so that the respectively neighboring circles 82 intersect.

On a center axis between two neighboring intersecting circles 82 andoutside the coupling shape, a further center of circle is set where acircle 84 with a larger radius Ri is drawn around it in each case. Therespective position of said outer, further center of circle as well asthe larger radius Ri are set such that the contour of the outer circle84 continuously merges with the contour of the two corner-side innercircles 82 and hence connects all neighboring corner circles 82 to eachother by forming a cavity. This means that the outer circle 84 istangential to the two inner corner circles 82 in the contact points,creating a continuous cross-sectional contour (without corners andedges) with four marked convex corner circles 82 and four smoothlyconcave side circles 84.

In geometrical terms, the cross-sectional contour can be definedaccording to the preferred exemplary embodiment as follows:

According to FIG. 14, the value A designates the diameter of acircumferential circle with a centric center of circle and radiallyouter contact points on all corner circles. The value B represents theclear measure between two opposing side circles, i.e. the diagonaldistance of those points on two opposing side circles which representthe innermost points on the cross-section.

Accordingly, these values A, B are in a proportion relative to eachother according to formula (1):

B=kB*A with 0.6<kB<0.9  (1)

The radius Re of each corner circle is in a proportion to the value Aaccording to formula (2):

Re=kRe*A with 0.6<kRe<0.9  (2)

The radius Ri of each side circle is in a proportion to the value Aaccording to formula (3):

Ri=kRi*A with 0.8<kRi<1.5  (3)

FIG. 15 shows that the male as well as the female coupling piece has acorresponding cross-sectional shape, with a specific oversize of thefemale coupling piece.

1.-10. (canceled)
 11. A surgical torque-transferring instrumentcomprising: a handpiece to which a handpiece shaft is flanged; and atool mounting in the handpiece or in the handpiece shaft for selectivelyreceiving a surgical tool which is rotatably supported in the handpieceshaft or can be rotatably supported therein, for axially securing thetool in the tool mounting as well as for transferring a torque to thetool, the tool mounting comprising: at least one entrainment shaft whichis formed like a sleeve at least in sections and comprises a proximalplug-in zone for a torsion rod, a distal torque-transferring zone forthe tool, and an axial locking zone for the tool, and a closure sleevesurrounding the entrainment shaft in a shiftable manner and rotatablefashion, said closure sleeve comprising a distal blocking section whichacts on the axial locking zone of the entrainment shaft for axiallylocking and releasing the tool, and a proximal arresting section actingon the plug-in zone of the entrainment shaft for arresting the toolmounting on the torsion rod to transfer torques and axial forces and forreleasing the tool mounting from the torsion rod.
 12. The surgicaltorque-transferring instrument according to claim 11 comprising at leastone entrainment element which is inserted in the plug-in zone in aform-fitting manner between the entrainment shaft and the torsion rodand is radially securable by the closure sleeve in an axial lockingposition.
 13. The surgical torque-transferring instrument according toclaim 12, wherein the at least one entrainment element comprises aplurality of entrainment elements in the form of balls, or in the formof rollers, cylinders or barrels rounded on the end face, theentrainment elements being located in accommodation pockets on the outercircumference of the torsion rod as well as in radial apertures oropenings in the plug-in zone of the closure sleeve in order to directlytransfer at least torques from the torsion rod to the entrainment shaft.14. The surgical torque-transferring instrument according to claim 13,wherein the closure sleeve has at least one fill opening provided at theproximal arresting section for inserting the entrainment elements in anaxial release position and a rotary filling position.
 15. The surgicaltorque-transferring instrument according to claim 11, wherein the distaltorque-transferring zone is formed by an axial longitudinal slit in theentrainment shaft which is formed like a sleeve in said portion,producing two axially extending protrusions or tongues which define atool mounting gap and are provided for a form-fitting connection with aninserted tool.
 16. The surgical torque-transferring instrument accordingto claim 15, wherein the axial locking zone is arranged in the proximalextension of the torque-transferring zone, said axial locking zonecomprising angularly spaced radial through-holes for receiving lockingelements in the form of balls which are pushed radially inwards by theclosure sleeve in an axial locking position.
 17. The surgicaltorque-transferring instrument according to claim 16, wherein theclosure sleeve has an inner radial widening at its distal end portionfor radially releasing the locking elements in an axial release positionand for filling the radial through-holes with the locking elements inthe axial release position and a rotary filling position.
 18. Thesurgical torque-transferring instrument according to claim 15 comprisingan accommodation chamber which is formed in the entrainment shaft, isdisposed proximal relative to the locking zone, and holds a followerelement which comprises an axial, bolt-shaped engagement portion beingurged in axial direction between the locking elements by an axiallyacting follower spring.
 19. The surgical torque-transferring instrumentaccording to claim 18, wherein the follower element is provided forurging the locking elements radially outward when the tool is notinserted and in doing so retaining the closure sleeve in its axialrelease position, and for being axially shifted against the followerspring by insertion of a tool in order to allow a radial inward motionof the locking elements for axially locking the tool as well as an axialdisplacement of the closure sleeve into its locking position in whichthe locking elements continue to be pushed radially inward against thetool.
 20. The surgical torque-transferring instrument according to claim11, wherein a torque introduced by the torsion rod is transferred to theat least one entrainment shaft through a number of entrainment elementswhich are circumferentially arranged on the torsion rod, and from saidentrainment shaft directly to a tool received in the entrainment shaft,the axial securement of the tool in the entrainment shaft being effectedby axially acting locking elements between the at least one entrainmentshaft and the tool (1).